Ethanol for industrial use is conventionally produced from petrochemical feed stocks, such as oil, natural gas, or coal, from feed stock intermediates, such as syngas, or from starchy materials or cellulosic materials, such as corn or sugar cane. Conventional methods for producing ethanol from petrochemical feed stocks, as well as from cellulosic materials, include the acid-catalyzed hydration of ethylene, methanol homologation, direct alcohol synthesis, and Fischer-Tropsch synthesis. Instability in petrochemical feed stock prices contributes to fluctuations in the cost of conventionally produced ethanol, making the need for alternative sources of ethanol production all the greater when feed stock prices rise. Starchy materials, as well as cellulosic material, are converted to ethanol by fermentation. However, fermentation is typically used for consumer production of ethanol, which is suitable for fuels or human consumption. In addition, fermentation of starchy or cellulosic materials competes with food sources and places restraints on the amount of ethanol that can be produced for industrial use.
Ethanol production via the reduction of alkanoic acids and/or other carbonyl group-containing compounds has been widely studied, and a variety of combinations of catalysts, supports, and operating conditions have been mentioned in the literature. During the reduction of alkanoic acid, e.g., acetic acid, other compounds are often formed with ethanol or are formed in side reactions. These impurities may limit the production of ethanol and may require expensive and complex purification trains to separate the impurities from the ethanol.
For example, U.S. Pat. No. 7,884,253 discloses methods and apparatuses for selectively producing ethanol from syngas. The syngas is derived from cellulosic biomass (or other sources) and can be catalytically converted into methanol, which in turn can be catalytically converted into acetic acid or acetates. The ethanoic acid product may be removed from the reactor by withdrawing liquid reaction composition and separating the ethanoic acid product by one or more flash and/or fractional distillation stages from the other components of the liquid reaction composition such as iridium catalyst, ruthenium and/or osmium and/or indium promoter, methyl iodide, water and unconsumed reactants which may be recycled to the reactor to maintain their concentrations in the liquid reaction composition. As another example, EP2060553 discloses a process for the conversion of a carbonaceous feedstock to ethanol wherein the carbonaceous feedstock is first converted to ethanoic acid, which is then hydrogenated and converted into ethanol. Also, U.S. Pat. No. 4,497,967 discloses an integrated process for the preparation of ethanol from methanol, carbon monoxide and hydrogen feedstock. The process esterifies an acetic anhydride intermediate to form ethyl acetate and/or ethanol. In addition, U.S. Pat. No. 7,351,559 discloses a process for producing ethanol including a combination of biochemical and synthetic conversions results in high yield ethanol production with concurrent production of high value co-products. An acetic acid intermediate is produced from carbohydrates, such as corn, using enzymatic milling and fermentation steps, followed by conversion of the acetic acid into ethanol using esterification and hydrogenation reactions. Also, U.S. Pub. No. 2010/0261800 discloses a process for the production of ethanol of ethanol from synthesis gas through methanol carbonylation to form ethanoic acid and esterifing ethanoic acid to methyl ethanoate and/or ethyl ethanoate.
In additional to alkanoic acids, methyl acetate can also be used to make ethanol. For example, U.S. Pat. No. 8,088,832 discloses a method and apparatus for synthesizing ethanol using stepwise catalytic reaction to convert carbon monoxide and hydrogen into ethanol through intermediates, such as methanol and methanol acetate, using catalysts including iridium acetate. U.S. Pat. No. 8,080,693 discloses a process for converting methanol to ethanol which comprises reacting methanol and carbon monoxide in the presence of a catalyst to produce a product comprising at least 25 mole % methyl acetate and, in some instances, acetic acid. U.S. Pat. No. 4,454,358 discloses a process for continuously producing ethanol via the carbonylation of methanol and hydrogenating a mixture of methanol and methyl acetate to form ethanol. Another route to ethanol is proposed by U.S. Pub. No. 2011/0124927 for converting syngas to dimethyl ether, carbonylating the dimethyl ether to methyl acetate, hydrogenating the methyl acetate to methanol and ethanol, and recovering the ethanol product.
In view of the conventional processes and literature, the need remains for improved ethanol production processes that are capable of effectively using methyl acetate, which may be formed from methanol and/or carbon monoxide feed sources.